Total Syntheses and Antibacterial Evaluations of Neocyclomorusin and Related Flavones.

Neocyclomorusin (1), a natural bioactive pyranoflavone mainly isolated from plants of the Moraceae family, was synthesized for the first time using a Friedel-Crafts reaction, a Baker-Venkataraman (BK-VK) rearrangement, a selective epoxidation, and a novel SN2-type cyclization as the key steps. The present protocol was also successfully applied for the total synthesis of oxyisocyclointegrin (2). Structurally related natural products morusin (23) and cudraflavone B (24) were also prepared. We investigated the antibacterial activities of these natural compounds against both Gram-negative and Gram-positive strains. The prenylated flavones, morusin (23) and cudraflavone B (24), showed comparable activity to ampicillin and kanacycin A against Staphylococcus aureus. Both morusin (23) and cudraflavone B (24) showed better antibacterial activities than ampicillin against the Gram-positive bacteria Staphylococcus epidermidis and Bacillus subtilis. Both neocyclomorusin (1) and oxyisocyclointegrin (2) displayed disappointing antimicrobial activities against Escherichia coli, Staphylococcus aureus, Staphylococcus epidermidis, and Bacillus subtilis strains.

Norwogonin attenuates hypoxia-induced oxidative stress and apoptosis in PC12 cells.

BACKGROUND: Norwogonin is a natural flavone with three phenolic hydroxyl groups in skeletal structure and has excellent antioxidant activity. However, the neuroprotective effect of norwogonin remains unclear. Here, we investigated the protective capacity of norwogonin against oxidative damage elicited by hypoxia in PC12 cells. METHODS: The cell viability and apoptosis were examined by MTT assay and Annexin V-FITC/PI staining, respectively. Reactive oxygen species (ROS) content was measured using DCFH-DA assay. Lactate dehydrogenase (LDH), malondialdehyde (MDA) and antioxidant enzyme levels were determined using commercial kits. The expression of related genes and proteins was measured by real-time quantitative PCR and Western blotting, respectively. RESULTS: We found that norwogonin alleviated hypoxia-induced injury in PC12 cells by increasing the cell viability, reducing LDH release, and ameliorating the changes of cell morphology. Norwogonin also acted as an antioxidant by scavenging ROS, reducing MDA production, maintaining the activities of superoxide dismutase (SOD), catalase (CAT) and glutathione peroxidase (GPx), and decreasing the expression levels of HIF-1α and VEGF. In addition, norwogonin prevented cell apoptosis via inhibiting the expression levels of caspase-3, cytochrome c and Bax, while increasing the expression levels of Bcl-2 and the ratio of Bcl-2/Bax. CONCLUSIONS: Norwogonin attenuates hypoxia-induced injury in PC12 cells by quenching ROS, maintaining the activities of antioxidant enzymes, and inhibiting mitochondrial apoptosis pathway.

Improved preparation of vitexin from hot water extract of Basella alba, the commercially available vegetable Malabar spinach ("Tsurumurasaki" in Japanese) and the application to semisynthesis of chafuroside B.

Hot water extraction of D-arabinofuranosylvitexin from the raw leaves of commercially available Basella alba "Tsurumurasaki" and subsequent acidic hydrolysis was improved to be a procedure using a high-pressure steam sterilizer to afford vitexin. The amount was estimated to be 14.1 mg from 1 g of dry weight of the raw leaves, whose recovery was calculated to be 95% based on the estimated content of D-arabinofuranosylvitexin in B. alba raw leaves. The product was dehydratively cyclized between hydroxy groups on the carbohydrate and flavone skeletons under modified Mitsunobu reaction conditions in N,N-dimethylformamide to give chafuroside B, which is known to be a bioactive Oolong tea polyphenol. Through these transformations, 10.2 mg of chafuroside B could be semisynthesized from 1 g of dry weight of the raw leaves, and the efficiency was improved compared to that from the extraction from Oolong tea (3.4 µg from 1 g of dry weight).

Preparation and in vitro antioxidant activity of some novel flavone analogues bearing piperazine moiety.

BACKGROUND: A series of eight new flavone derivatives containing a piperazine chain with different substitution were synthesized and their structures were determined. METHODS: Their antiradical and antioxidant activities were evaluated using superoxide anion radical, hydroxyl radical, 2,2-diphenyl-1-picrylhydrazyl radical, 2,2'-azino-di(3-ethylbenzthiazoline sulphonate) radical cation (ABTS+) scavenging (as measure total antioxidant status TAS), ferric reducing antioxidant power (TAC), and hydrogen peroxide decomposition. The antioxidant activities of the synthesized compounds were compared with standard antioxidants trolox, ascorbic acid, butylated hydroxytoluene (BHT) as positive controls, reference antibiotics (doxycycline, dicloxacillin), and medicinal plants (Menthae piperita, Cistus incanus). Chemiluminescence, spectrophotometry, electron spin resonance (ESR) spectroscopy in conjunction with 5,5-dimethyl-1-pyrroline-1-oxide (DMPO) as the spin trap were the measurement techniques. RESULTS: The results show that the synthesized compounds exhibit weak, albeit a wide spectrum of antiradical and antioxidant activities. The TAS values were measured as trolox equivalents, ranging from 209.6 ± 6.1 to 391.1 ± 8.2 µM TE/g; the TAC values were in ranges from 10.8 ± 0.5 to 49.5 ± 0.5 µM TE/g being higher than that of dicloxacillin (241.0 ± 16.5 and 9.73 ± 0.8 µM TE/g, respectively), but lower than ascorbic acid, BHT, doxycycline, and medicinal plants. Best antioxidant activities were found for the piperazinyl analogues with methoxy group on phenyl piperazine ring. CONCLUSION: We suggest that the synthesized compounds may be used as lead molecules for optimization of molecular structure to maximize the antioxidant potency.

Furanoflavones pongapin and lanceolatin B blocks the cell cycle and induce senescence in CYP1A1-overexpressing breast cancer cells.

Expression of cytochrome P450-1A1 (CYP1A1) is suppressed under physiologic conditions but is induced (a) by polycyclic aromatic hydrocarbons (PAHs) which can be metabolized by CYP1A1 to carcinogens, and (b) in majority of breast cancers. Hence, phytochemicals or dietary flavonoids, if identified as CYP1A1 inhibitors, may help in preventing PAH-mediated carcinogenesis and breast cancer. Herein, we have investigated the cancer chemopreventive potential of a flavonoid-rich Indian medicinal plant, Pongamia pinnata (L.) Pierre. Methanolic extract of its seeds inhibits CYP1A1 in CYP1A1-overexpressing normal human HEK293 cells, with IC50 of 0.6 µg/mL. Its secondary metabolites, the furanoflavonoids pongapin/lanceolatin B, inhibit CYP1A1 with IC50 of 20 nM. Although the furanochalcone pongamol inhibits CYP1A1 with IC50 of only 4.4 µM, a semisynthetic pyrazole-derivative P5b, has ∼10-fold improved potency (IC50, 0.49 µM). Pongapin/lanceolatin B and the methanolic extract of P. pinnata seeds protect CYP1A1-overexpressing HEK293 cells from B[a]P-mediated toxicity. Remarkably, they also block the cell cycle of CYP1A1-overexpressing MCF-7 breast cancer cells, at the G0-G1 phase, repress cyclin D1 levels and induce cellular-senescence. Molecular modeling studies demonstrate the interaction pattern of pongapin/lanceolatin B with CYP1A1. The results strongly indicate the potential of methanolic seed-extract and pongapin/lanceolatin B for further development as cancer chemopreventive agents.

Convenient Synthesis and Physiological Activities of Flavonoids in Coreopsis lanceolata L. Petals and Their Related Compounds.

Chalcones, flavanones, and flavonols, including 8-methoxybutin isolated from Coreopsis lanceolata L. petals, were successfully synthesized with total yields of 2⁻59% from O-methylpyrogallols using the Horner⁻Wadsworth⁻Emmons reaction as a key reaction. Aurones, including leptosidin, were also successfully synthesized with 5⁻36% total yields using the Aldol condensation reaction as a key reaction. Each chalcone, flavanone, flavonol, and aurone with the 3,4-dihydroxy groups in the B-ring showed high antioxidant activity. Additionally, each of the chalcones, flavanones, flavonols, and aurones with the 2,4-dihydroxy groups in the B-ring showed an excellent whitening ability.

Synthesis and in vitro Antioxidant Activity Study of Some Novel Substituted Piperazinyl Flavone Compounds.

BACKGROUND: A new series of 13 piperazinyl flavone derivatives has been synthesized and examined for their in vitro antiradical and antioxidant activities in response to the pharmacy industry's increasing demand for new non-toxic anti-inflammatory and anticancer drugs. METHOD: Their antioxidant activity was evaluated by the reactive oxygen species (ROS) scavenging assays, 2,2-diphenyl-1-picrylhydrazyl free radical (DPPH•) and 2,2'-azino-bis(3- ethylbenzothiazoline-6-sulphonic acid) radical cation (ABTS+•) scavenging assays, and the ferric reducing antioxidant potency (TAC) method, and was compared to known positive controls, herbal infusions, and penicillins. Chemiluminescence, spectrophotometry, electron spin resonance (ESR) and 5,5-dimethyl-1-pyrroline-1-oxide (DMPO) as the spin trap were the measurement techniques. RESULT: It was seen that synthesized compounds have a wide spectrum of antioxidant property. Some of the test compounds proved to be extremely efficient scavengers of H2O2 exhibiting, in some cases, EC50 of about 2 µM. The values of antioxidant status (TAS) were in the range of 49 ± 3.9 to 1283 ± 51.3 µM TE/g (TE = Trolox equivalent) and were lower than that of butylated hydroxytoluene (BHT) (1304 ± 43.2 µM TE/g) and green tea (1356 ± 40.0 µM TE/g), but for several synthesized compounds, they were higher than chamomille infusion and penicillins. Ferric reducing antioxidant powers (TAC) for the piperazinyl flavone derivatives were in the range 7 ± 0.5 to 104 ± 0.6 µM TE/g and were weaker than that of BHT (217 ± 5.3 µM TR/g ). CONCLUSION: Carboxylic or hydroxamic acid substituted piperazinyl flavones are potentially active as antioxidants, thus may be suggested as pharmacologically interesting ones.

Semisynthetic Flavone-Derived Antimicrobials with Therapeutic Potential against Methicillin-Resistant Staphylococcus aureus (MRSA).

A new series of semisynthetic flavone-based small molecules mimicking antimicrobial peptides has been designed from natural icaritin to combat drug-resistant Gram-positive bacterial infections. Compound 6 containing two arginine residues exhibited excellent antibacterial activity against Gram-positive bacteria, including MRSA, and very low toxicity to mammalian cells, resulting in a high selectivity of more than 511, comparable to that of several membrane-active antibiotics in clinical trials. Our data show for the first time that icaritin derivatives effectively kill bacteria. Meanwhile, this is the first study deploying a biomimicking strategy to design potent flavone-based membrane targeting antimicrobials. 6 showed rapid bactericidal activity by disrupting the bacterial membrane and can circumvent the development of bacterial resistance. Importantly, 6 was highly efficacious in a mouse model of corneal infection caused by MRSA and Staphylococcus aureus.

Efficient synthesis of polymethoxyselenoflavones via regioselective direct C-H arylation of selenochromones.

Substantial research has suggested that the configuration and the total number of functional groups on flavones influence their bioactivity. To investigate the changes in the biological activities of selenoflavones in relationship to structural changes, the development of a generally applicable synthetic method was a key. Until now, an efficient pathway for palladium-catalyzed direct arylation with the selenocyclic enone systems is not known in the literature. We herein introduce a simple direct C-H arylation of two difficult coupling partners, selenochromones and electron-rich aryl bromide, affording diverse polymethoxyselenoflavones with great efficiency and high selectivity.

Synthesis of Effective Food Constituents toward the Development of Chemical Biology Investigations.

This article describes the development of various probes and immunogens for chemical-biological investigations of food flavonoids. We accomplished a large (gram)-scale asymmetric synthesis of a key intermediate, 5-aminopentyl deoxy epigallocatechin-3-gallate (APDOEGCg; 3), an analogue of green tea polyphenol EGCg, in which the key step was cationic cyclization utilizing neighboring group participation of the gallate carbonyl group. The synthetic APDOEGCg (3) was efficiently converted to a fluorescent probe 18 and an immunogen 19 by utilizing the high reactivity of the amine functional group. We confirmed the usefulness of these probes for imaging studies and the generation of antibodies, respectively. We also describe the efficient synthesis of a positron emission tomography (PET) probe [11C]20 by incorporation of 11C into EGCg (1), for which synthetic 4″-Me-EGCg (20) was utilized as an authentic sample. Our synthetic strategy was also applied for the practical synthesis of nobiletin (21), a polymethoxylated flavone from citrus. Synthetic nobiletin was readily converted to various probes by selective demethylation and incorporation of fluorescein, biotin or 11C. These probes should be useful for a range of biological applications. Detailed examination of the mechanisms and further applications are in progress.

Facile synthesis of acacetin and its derivatives.

Acacetin, a O-methylated bioflavonoid isolated from the traditional Chinese medicine Xuelianhua (Saussurea tridactyla), is a promising orally effective atrium-selective antiarrhythmic agent for the treatment of atrial fibrillation (AF). Here we describe an efficient two-component method for the synthesis of acacetin and its derivatives.

Synthesis of a highly water-soluble acacetin prodrug for treating experimental atrial fibrillation in beagle dogs.

We previously reported that duodenal administration of the natural flavone acacetin can effectively prevent the induction of experimental atrial fibrillation (AF) in canines; however, it may not be used intravenously to terminate AF due to its poor water-solubility. The present study was to design a water-soluble prodrug of acacetin and investigate its anti-AF effect in beagle dogs. Acacetin prodrug was synthesized by a three-step procedure. Aqueous solubility, bioconversion and anti-AF efficacy of acacetin prodrug were determined with different methodologies. Our results demonstrated that the synthesized phosphate sodium salt of acacetin prodrug had a remarkable increase of aqueous solubility in H2O and clinically acceptable solution (5% glucose or 0.9% NaCl). The acacetin prodrug was effectively converted into acacetin in ex vivo rat plasma and liver microsome, and in vivo beagle dogs. Intravenous infusion of acacetin prodrug (3, 6 and 12 mg/kg) terminated experimental AF without increasing ECG QTc interval in beagle dogs. The intravenous LD50 of acacetin prodrug was 721 mg/kg in mice. Our preclinical study indicates that the synthesized acacetin prodrug is highly water-soluble and safe; it effectively terminates experimental AF in beagle dogs and therefore may be a promising drug candidate for clinical trial to treat patients with acute AF.

Convergent synthesis of moslosooflavone, isowogonin and norwogonin from chrysin.

A convergent synthesis route of moslooflavone, isowogonin and norwogoninis reported,starting from chrysin, an easily available flavone, by methylation, bromination, methoxylation and demethylation procedures. This synthetic route is convenient and can give the three rare flavones in good yield.

Design and synthesis of azaisoflavone analogs as phytoestrogen mimetics.

A series of azaisoflavone analogs were designed and synthesized and their transactivation activities and binding affinities for ERα and ERß were investigated. Among these compounds, 2b and 3a were the most potent with 6.5 and 1.1 µM of EC50, respectively. Molecular modeling study showed putative binding modes of the compound 3a in the active site of ERα and ERß, which were similar with that of genistein and provided insight of the effect of N-alkyl substitution of azaisoflavones on ERß activity. Also, a biphasic effect of azaisoflavone analogs on MCF-7 cell growth depending on their concentrations was investigated.

Discovery and characterization of synthetic 4'-hydroxyflavones-New CK2 inhibitors from flavone family.

Human protein kinase CK2 is one of the most intriguing enzymes, which functional role still remains unclear despite of decades of studying. At present there is abundant evidence pointing to the fact that inhibitors of CK2 could be used as pharmaceutical agents to treat cancer, viral infections and inflammatory diseases. Here we report novel synthetic flavone inhibitors, 4'-hydroxyflavones, possessing high activity towards CK2. These compounds were identified with receptor-based virtual screening and then chemically optimized on the base of rationale derived from biochemical screening and molecular modeling. It has been demonstrated that synthetic flavone derivatives are much more potent CK2 inhibitors than the natural ones, and we believe that their further examination will be helpful for studying biological role of CK2 as well as for development of new kinase-oriented drugs.

Evaluation of coumarin and neoflavone derivatives as HCV NS5B polymerase inhibitors.

Coumarins and coumestans represent an important family of compounds with diverse pharmacological properties. We recently identified coumestans as novel inhibitors of hepatitis C virus NS5B polymerase and predicted their binding in thumb pocket-1 (TP-1) of NS5B. As the coumarins are structurally related to coumestans by virtue of their common A- and B-rings, we postulated them to also exhibit similar binding interaction with NS5B and inhibit its polymerase function. We therefore investigated 24 coumarin and neoflavone derivatives as candidate NS5B inhibitors and identified 14 compounds inhibiting NS5B polymerase activity with IC50 values between 17 and 63 µm. Of these, the newly synthesized 6,8-diallyl-5,7-dihydroxycoumarin (8a) was produced in three steps in high chemical yield from floroglucinol and found to be the most potent of this series, exhibiting activity similar to the reference coumestan LQB-34. The binding site of 8a was mapped to TP-1 of NS5B by counter screening against P495L NS5B mutant, employed as a screen for TP-1 site binders. NS5B-TP-1-8a interaction map provided insight into 8a binding and offered clues for future SAR optimization.

Methylenebissantin: a rare methylene-bridged bisflavonoid from Dodonaea viscosa which inhibits Plasmodium falciparum enoyl-ACP reductase.

A new methylene-bridged bisflavonoid, methylenebissantin (1), and nine known compounds, including flavonoids (2-5), diterpenoids (6 and 7), and phenol derivatives (8-10) were isolated from the aerial parts of Dodonaea viscosa Jacq. The structure elucidation was based on spectroscopic data analyses. The isolated compounds were evaluated for the inhibition of Plasmodium falciparum enoyl-ACP reductase (PfENR). Methylenebissantin (1) exhibited a moderate inhibition (IC(50) 91.13 µM) against PfENR.

Synthesis of antiproliferative flavones from calycopterin, major flavonoid of Calycopteris floribunda Lamk.

Eighteen new analogues of 5,3'-dihydroxy-3,6,7,8,4'-pentamethoxy-flavone, a potent natural cytotoxic and antimitotic flavone, were synthesized from calycopterin, the major flavonoid of Calycopteris floribunda Lamk., a traditional Asian medicinal plant. One of them, the 3'-amino substituted analogue, displayed almost the same activity as the reference compound. Pharmacomodulation at C-3' on the B-ring, and at C-5,6,7 and 8 on the A-ring allowed to refine structure-activity relationships within the cytotoxic flavones series.

Discovery and synthesis of novel luteolin derivatives as DAT agonists.

Luteolin, 5,7-dihydroxy-2-(3,4-dihydroxyphenyl)-4H-chromen-4-one, has been proposed and proved to be a novel dopamine transporter (DAT) activator. In order to develop this potential of luteolin, a series of novel luteolin derivatives were designed, synthesized, and evaluated for their DAT agonistic activities, utilizing constructed Chinese hamster ovary (CHO) cell lines stably expressing rat DAT. Biological screening results demonstrated that luteolin derivatives 1d, 1e, and 4c carry great DAT agonistic potency (EC(50)=0.046, 0.869, and 1.375µM, respectively) compared with luteolin 8 (EC(50)=1.45±0.29µM). Luteolin derivative 1d, notably, exhibited a 32-fold-higher DAT agonistic potency than luteolin. These luteolin derivatives represent a novel DAT agonist class, from which lead compounds useful for exploration of additional novel DAT agonists could be drawn.

In-situ absorption, protein binding and pharmacokinetic studies of S002-853, a novel antidiabetic and antidyslipidaemic flavone derivative in rats.

OBJECTIVES: The aim of the study was to investigate the in-situ absorption kinetics, plasma protein binding and pharmacokinetic characteristics of a novel synthetic flavone derivative, S002-853, which shows pronounced antidiabetic and antidyslipidaemic activity. METHODS: Quantification of S002-853 in plasma was performed by the LC-MS/MS method and in-situ sample analysis was carried out by the HPLC-UV method. KEY FINDINGS: The absorption rate constant was 0.274/h in a mild alkaline environment, which S002-853 experiences in the intestine following oral dose administration. Plasma protein binding was found to be 26.37 +/- 2.58% at a concentration of 1 microg/ml. The pharmacokinetic parameters were determined in male rats after administration of a single 40 mg/kg oral dose and 10 mg/kg intravenous dose. The peak plasma concentration (C(max)) was found to be 60.93 ng/ml at 8 h after oral administration. Irregular concentration-time profiles with secondary peaks were observed after oral dose administration. The elimination half-life of the compound was 19.56 h and 16.30 h after oral and intravenous doses, respectively. Comparison of the AUC after oral and intravenous dosing of S002-853 indicates that only about 29.48% (bioavailability) of the oral dose reaches the systemic circulation. CONCLUSIONS: In-situ study of S002-853 shows slow absorption from the gastrointestinal tract. S002-853 also shows low plasma protein binding. The pharmacokinetic parameters after oral and intravenous dose reveal low oral bioavailability and high mean residence time.